Unemployment Runs Rampant with New Technology
Flight Management Systems
By Jim Sparks
November 1999
Back in the beginning, there was man and machine. Little else was needed as aviators of the day need only stay in sight of the ground to provide themselves with navigation queues.
Early on, a well-equipped aircraft had an altimeter, compass, airspeed indicator, and maybe several engine indicators. Fuel quantity was not a problem — when the engine would start to sputter, the pilot could find a farmers field or an unoccupied roadway. Then, after landing, most passersby would volunteer fuel or at least supply the flier with a lift to the nearest service station, (providing the aviator would discuss his feats of aerobatics and barnstorming), and perhaps supply the awestruck deliverer of fuel with a much sought after ride in an amazing flying machine. It soon became apparent that aviation had some commercial value, so the development of aircraft for the purpose of hauling not only people but also cargo was soon realized.
Of course, with that came equipment to combat the obstacles that blinded the flier from his visual means of navigating. Gyro systems were being employed to reflect attitude and heading, and radio navigation systems were being developed so a properly equipped aircraft could fly day or night and even in some types of foul weather conditions. The need rapidly arose for aircraft to fly faster and farther with larger payloads and with the ability to safely conduct the flight in all but the worst weather conditions.
Airliners that precluded the jet age were equipped with a crew of specialists that mirrored the maritime industry. The pilot assumed the rank of Captain and was in charge of the aircraft. The First Officer was second in command and would make the decisions in the Captain's absence. In addition to decision making, it was the responsibility of these two to fly the aircraft. Most large four engine aircraft of the day would carry a systems specialist called the Flight Engineer. It would be his responsibility to monitor the engines and make the needed adjustments. He could also be called upon to provide the Captain with information regarding fuel burn and remaining fuel as well as observe other aircraft systems to insure proper operation.
A Load Master was another important member of the team. It was the responsibility of this person to insure the proper loading of fuel and cargo and then calculate the weight and balance, as this would have to be factored into published charts to determine runway length and flap settings. The Navigator was also considered essential on most long haul flights as radio navigation equipment of the day was not in place or its operation was intermittent. Practicing the science of celestial navigation, or by plotting times and distances to radio stations, the navigator could supply the captain with an accurate position as well as information on time to destination.
Communications were routinely handled by the Communications Officer. It was his job to have all required ground station frequencies for the departure airport as well as enroute contacts and the arrival airport. This crewmember would also possess any specially designated company frequencies and codes that could be used to communicate with headquarters or with other airborne company aircraft. All frequency selections would be controlled by this person as well as the directing of the ground to air calls to the appropriate crewmember.
Advancements in avionics technology soon displaced the likes of the communications office, navigator, load master, and even the flight engineer. Newer flight decks presented information to the pilot and copilot using methods that did not require constant monitoring. The forward progress in the development of auto pilot systems soon gave the pilot and copilot a dramatic reduction in workload. Even new electronic radio navigation systems provided a very precise position, and could even be coupled into the autopilot, enabling the crew to automatically fly from one radio beacon transmitter to another or to obtain an accurate position fix from an inertial navigation system. Doppler radar was even being used to map terrain and spot specific geographic targets.
Aircraft of today manage to fly one-third of the way around the world with a flight crew of two or three. This is all made possible through tremendous advancements in aviation technology including full function automatic flight control systems; where navigation and engine thrust management are handled without the need for continuos pilot intervention. Newer aircraft incorporate systems that utilize a means of identifying faults and in some cases taking an appropriate corrective action thereby relieving the flight crew of this duty.
Much of the reduction in the workforce needed to operate an aircraft in flight is a direct result of the Flight Management System (FMS). Typically, these units can provide numerous functions including selecting and monitoring navigation systems, communications with the automatic flight control system, thrust management, operation of warning display systems, automatic tuning of navigation and communication radios, weight and balance computations, as well as performance calculations. Simply stated, an FMS is a digital computer that can interact with the majority of navigation, communication and autoflight systems on the aircraft as well as maintain a database.
Most FMS are comprised of a Control Display Unit (CDU) and one or more computers. Some systems include separate navigation and performance computers, yet enable them to communicate on an Avionics Standard Communication Bus (ASCB) so that joint use information can be displayed.
The electrical power requirements will vary depending on the type unit and which aircraft it is installed. It is important to note that frequently the primary electrical power is backed up with a dedicated storage battery, and in some cases will remain energized anytime the aircraft is weight off wheels. This is an important consideration prior to jacking an aircraft with an FMS installed.
The Control Display Unit (CDU) provides the primary means for the flight crew to communicate with the system. It also provides a display where computer information can be manifested. In some cases, this is a monochromatic display while other systems use full color. Frequently brightness controls are installed to adjust for the effects of clouds or sunlight. Most CDUs include a full alphanumeric keyboard as well as line keys to facilitate data entry and reduce keystrokes while in flight.
The navigation computer is the component that provides both vertical and lateral position information and incorporates an internal database of varying sizes. This database is used for the storage of waypoints, Nav aids, routes, airports, Nav data, communication data, Standard Instrument Departures (SID), Standard Arrival Routes (STAR), and NOTAMS. The data base can also be used to store frequently used flight plans.
As navigation routes frequently change, pilots are required to update their charts once every 28 days. The database for an FMS will require the same maintenance. Fortunately, many systems have a Data Loader, which makes transfer of electronic media an easy task. In other systems, a laptop computer can be employed as a tool for communicating with and updating the internal database.
Fuel on board is one of the primary requirements of the Performance Computer. In some systems, this data is automatically fed from the aircraft fuel quantity indicating system but still requires recognition by the flight crew via a keystroke on the CDU. A fuel flow sensor will also be used by the performance computer to calculate aircraft gross weight, as well as specific range in nautical miles per pound of fuel.
Most current day FMS are designed to fit a wide range of aircraft. Some with two engines, some with three, and some with four. The system is capable of receiving fuel flow data from up to four engines and will need to be programmed for the number of engines installed on a specific aircraft.
The other significant factor in predicting range is ground speed, which is provided by the navigation computer. Some flight management systems include load cells installed on each landing gear. This feature will provide for weight and balance calculations. In some cases, wheel speed sensors installed in the nose or main wheel axles supply a ground speed reference to start the performance calculations. In other cases, airspeed is used to tell the system to come to life.
A Performance Data page is usually provided to show the crew a summary of predictions such as Estimated Time En route (ETE), Estimated Time Arrival (ETA), fuel remaining and gross weight. In addition, performance estimates on optimum altitudes, cruise modes, step climbs, and "What If?" situations can be calculated. These calculations can even reflect wind speeds and directions.
On "power up," the CDU display sequence for pre-flight is prompted and usually includes the Greenwich Mean Time (GMT) clock and initial position information. In order to continue, the time and position need to be recognized individually. This is accomplished by entering latitude and longitude by keystrokes on the CDU. Once initialized, position data can be supplied to Inertial Reference Systems to aid in their alignment. If the date entered corresponds to the effective date of the database, access will be allowed to continue flight planning.
The FMS then leads the pilot to the next logical steps in the programming sequence. A flight plan can be loaded from an optional data loader. Prefabricated flight plans are available from various flight planning services or may be created on a computer using software provided by the FMS manufacturer.
The navigation function computes the aircraft position and velocity in all phases of flight. This is accomplished by selecting specific sensors or blending information from a group of sensors. The priority of navigation sensors is based on accuracy. The Global Positioning System (GPS), or satellite navigation, is the most accurate and when available, will provide 100 percent of the FMS. Even with GPS availability, other sensors are still monitored for position differences.
Distance Measuring Equipment (DME) is the next most accurate and an FMS can automatically tune and scan two DMEs to provide the best position from DME/DME. Very High Omni Directional Range (VOR) can also be used in conjunction with DME, but is less favored than DME/DME because with VOR, there may be a bearing error increasing in distance from the navigation station.
Long range navigation blending is where the FMS blends the data from the various long range navigation sensors. This is used when the aircraft is over water or in an area where there are few navigation aids. In this situation, the FMS evaluates the information from each sensor and determines the best position. Should any sensor differ from FMS calculated position by more than 10 Nautical Miles (NM), a position message will be displayed. In the event all means of radio navigation are lost, the FMS can determine its position by averaging position data from the Inertial Reference Systems.
A typical transoceanic flight may begin with DME/DME and as the aircraft leaves radio range, it would transition to IRS navigation and eventually long range blending or an established average IRS position. As the aircraft nears land, the system returns to radio updating. For a GPS-equipped aircraft, additional sensors are only monitored and satellite navigation is used entirely.
In addition to being able to auto tune navigation radios, many FMS can provide tuning capabilities for communication radios.
In short, an FMS is an all-encompassing Area Navigation (RNAV) system with the ability to provide the pilot visual queues on how to steer the aircraft over predetermined way points to a specific destination, while at the same time providing information on fuel status and time and distance. This system can also be coupled to an automatic flight control system, which can even provide thrust management predicated on time and cost and can calculate vertical angles of ascent and decent.
With the onset of FMS, we have eliminated the need for navigators, communication officers, and in some cases, load masters and flight engineers.
Who knows, maybe the flight crew of the future will be a pilot and a dog. The pilot's only task will be to feed the dog and the dog's purpose is to bite the pilot if he touches anything except the dog food.
